The present invention relates to novel pigments, and in particular, pigments that have been treated with certain organo-phosphoric acid compounds and/or their salts.
The incorporation of pigments into polymer matrices has been performed for many years, and over the years, pigments have been and continue to be incorporated into polymer matrices for many reasons. For example, pigments may be used as fillers. They may also be used to impart better physical and chemical attributes to polymer matrices, including improved thermal stability, especially lacing resistance in extruded polymer film applications, and decreased chemical activity. In order to obtain different benefits, pigments may be treated in different ways, including by adding surface treatments.
Commonly used pigments include titanium dioxide, kaolin and calcium carbonate. Commonly known surface treatments that have been applied to pigments include silanes, alkylphosphonic acids and phosphorylated polyenes.
The precise attributes that one wants in a treated pigment will depend in part on the application in which it will be used. Often one wants to provide a hydrophobic pigment that is stable, easy to prepare, cost effective, can be dispersed to a high degree in polymers, and does not react in the presence of other additives such as lithopone. However, despite the numerous known surface treatments, for various reasons, including cost and desired properties, no known surface treatments are ideal for all applications. Thus, there is always a need to develop new and better treatments for pigments.
One under-explored option for treating pigments is the use of organo-phosphoric acids, including the esters of phosphoric acids and their corresponding salts. These compounds have been suggested as useful when mixed in relatively large amounts with pigments and to form suspensions in, for example, aqueous coatings applications. However, such a use produces a unique product that may be used only in a limited application. Thus, the teachings for the use of relatively large amounts of esters of phosphoric acids in aqueous coatings applications do not suggest the treatment of pigments with low levels of the organo-phosphoric acids of this invention or that the pigments treated with the low levels of the organo-phosphoric acids of this invention would have utility in plastics.
The present invention provides economical and easily prepared novel pigments that possess resistance to lacing when incorporated into polymeric articles (such as films), do not produce objectionable side reactions when mixed with common plastics additives such as lithopone, which contains zinc sulfide, and are stable such that they possess low levels of extractable organics. Further, durable plastics products that incorporate the treated pigments of the present invention are likely to resist yellowing when phenolic-type antioxidants are used.